The present invention relates to a circuit for a device to measure the flowrate of electrically charged fluids and includes (1) a pipe section through which the fluid flows, (2) electromagnets, (3) at least two current sources connected to the electromagnets which cause the electromagnets to generate a magnetic field which extends through the pipe section, (4) at least two electrodes whose axes are connected by an imaginary line which extends through the fluid flow for the measurement of the electrical potential due to charge differential in the fluid flow, and (5) a correction circuit to which signals generated by the electrodes are connected and which produces an output signal proportional to the flowrate which is only minimally influenced by the flow profile and/or the level of the fluid in the pipe section.
A known circuit, described in DE-OS 27 43 954, has two electromagnets which, in relation to each other, can be turned on or off or reversed to change the magnetic field and thereby develop a correction function from the signals coming from the electrodes. The arrangement produces an output signal corresponding to the flowrate of the fluid in the pipe section which is essentially independent of the flow profile.
Another known circuit, described in EP-0451 308 A1, contains two pairs of electrodes with which flowrate measurements are made even if the pipe section is not full. Two electromagnets are provided which, relative to each other, can be turned on or off or reversed. By means of a correction function, an output signal is developed which is essentially independent of the flow profile in the flow stream and/or the level of the fluid in the pipe section.
Both circuits require, in addition to a normal magnet excitation, at least one other dissimilar magnet excitation in order to correct the output signal by means of a correction circuit. Because of the requirement for different magnet excitations, the response time, relative to that for single magnet excitation, is increased.